Beam deflecting apparatus with deflection coils located within an electron microscope specimen chamber



BEAM DEFLECTING APPARATUS WITH DEFLECT ION COILS LOCATED WITHIN AN ELECTRON MICROSCOPE SPECIMEN CHAMBER Filed Bpt. 2Q, 1966 y 1969 SHIGERU SUZUKI ET AL 3,445,652

IgYENT OR M a Wd-M/ M-' United States Patent US. Cl. 250-495 Claims ABSTRACT OF THE DISCLOSURE An electron beam deflecting apparatus for an electron microscope in which two electron beam deflection coils are arranged in a main specimen chamber such that the second deflection coil is oriented as nearly as possible to the specimen for deflecting the incident electron beam at as small an angle as possible with respect to the optical axis.

This application relates to beam deflecting apparatus for electron microscopes and more particularly to improvements in deflecting coil systems for electron microscopes.

In order to effectively examine crystalline specimens by an electron microscope a dark field image rather than a bright ifleld image is particularly useful. Contrast developed in a dark field image is created by variations in intensity due to variations in the positions of the atoms in the crystalline specimen. Any displacements of the atoms from the usual positions will produce a phase difference between beams which are diffracted from successive scattering centers. As a result dark field image techniques make it possible to observe defects, distortions, grain boundaries, stacking faults and strains due to precipitation, etc., which correspond to a given defraction pattern.

A dark field image can be produced either by tilting the incident beam or by inserting a suitably sized objective aperture in the back focal plane of the objective lens. In this latter case, the direct beam is stopped by the aperture. However, the presence of nonparallel rays adversely affects image formation. Tilting the incident beam will be most effectively obtained by means of a deflecting coil system and if a double deflecting coil system is used, a dark field image of high resolution can be obtained.

When using a double deflecting coil system, it is preferable to position the second deflection coil as near as possible to the specimen in order to deflect the incident beam at as small an angle as possible by means of a low power deflecting magnetic field.

In the conventional electron microscope changing specimens in the specimen chamber is difficult because of the arrangement of the second deflection coil. As a result, strong magnetic fields are required in order to deflect the incident electron beam at a pre-determined angle with respect to the optical axis, thus requiring a large and bulky deflection system.

The object of the present invention is to improve means for forming a high resolution dark field image in which the difliculties in conventional electron microscopes 'are avoided. An electron microscope embodying our invention has at least one of the deflecting coils within the main specimen chamber and at the same time specimens can be changed in the chamber by simply moving the deflecting coil within the chamber. The improved microscope also has means for changing specimens in which the deflecting coil is combined with an air locking system between the ice main specimen chamber and an auxiliary specimen chamber.

In the accompanying drawings we have illustrated certain presently preferred embodiments of our invention in which:

FIGURE 1 is a partial longitudinal section of an electron microscope showing that portion of the housing of the microscope in which beam deflection coils are mounted in accordance with our invention; and

FIGURE 2 is a similar view showing a modified form of our invention.

Referring now to FIGURE 1, a housing 1 forms part of an evacuated column 3 of an electron microscope. The housing contains condenser lens 10 and a specimen stage 20. A casing 2 for an auxiliary specimen chamber is positioned between the condenser lens 10 and the specimen stage.

A first deflection coil assembly 4 comprises a coil 5 having a passage 6 for electron beams extending through the center of the coil. The assembly 4 is mounted on a flange 11 which forms part of the condenser lens 10 and the assembly is positioned coaxially with the optical axis of the microscope by spools 7 and 8 and a yoke 9 all of which are of non-magnetic material.

Within the casing 2 there is an auxiliary specimen chamber 13 having a cover 12 which closes an opening 14 in the casing. The cover 12 is sealed to the casing 2 by an O-ring 18' so that a vacuum can be maintained within the chamber 13.

A rod 15 for changing specimens is mounted on a ring 17 positioned in the cover 12 so that it can be rotated and moved in all directions. The ring 17 is sealed by an O-ring 16. The rod 15 is used to change specimens by inserting and removing a specimen cartridge 19 into and from the specimen stage 20.

A casing 21 having a central aperture 22 for the electron beam is housed within the main specimen chamber 32 which extends transversely of the column 3 with its inner end opposite the auxiliary specimen chamber 13. The casing 21 is supported in the main specimen chamber by an arm 30 and sleeve 31 and can be rotated within the specimen chamber and also moved longitudinally in the chamber. The inner end of the casing 21 carries a cover 23 secured to it by screws 24. Upon movement of the casing 21 to the right (viewing FIGURE 1) the cover 23 engages the casing 2 and separates the main specimen chamber 32 from the auxiliary specimen chamber 13.

The rod 30 also carries a second deflection coil assembly 26 which comprises a coil 27, a spool 29, a yoke 28 and an aperture 25. The aperture 25 when in operating position is in line within the optical axis of the microscope. The outer end of the rod 30 carries a knob 33 and rotation of the knob rotates the rod 30* and the second deflection coil assembly 26. A guide plate 45 of nonmagnetic material enables the casing 21 to be easily moved longitudinally in the main specimen chamber 32 by the arm 30.

The specimen cartridge stage 20 which supports the specimen cartridge 19 includes a disc 34 which is supported by ball bearings 35 on a flange 36 of an objective lens 37 so that it can be moved on the flange 36.

The lower end of the specimen cartridge 19 extends within the objective lens pole pieces 38 and 39 of the microscope. These pole pieces have apertures 40 and 41 respectively, and :are separated by a cylinder 42 of nonmagnetic material. The objective lens 37 has a coil 44 which is wound around a spool 43 and extends between the flange 3-6 and another flange (not shown) of the objective lens.

In order to seal the main specimen chamber 32 at the point where the rod 30 extends outside the instrument and to hold the deflection coil assembly in selected positions, a collar 47 is threaded onto a boss 46 and carries a handle 48 whereby it can be tightened on the boss 46.

In the operation of the instrument, the casing 21 is positioned as shown in FIGURE 1 in the main specimen chamber 32. and the auxiliary specimen chamber 13 is closed by the cover 23. Also, the collar 47 is tightened on the boss 46 so that a vacuum can be maintained within the main specimen chamber 32. The specimen cartridge U carried on the rod 15 is inserted into the auxiliary specimen chamber 13 through the opening 14 and the cover 12 is closed. Thereafter, the auxiliary specimen chamber 13 is evacuated by suitable means. The handle 48 is turned to remove the collar 47 from the boss 46 and the knob 33 is rotated a suflicient amount (for example 180") and is pulled toward the outer end of the main specimen chamber 32. This moves the casing 21 and cover 23 away from the auxiliary specimen chamber 13. This makes it possible to place the specimen cartridge 19 on the cartridge stage 20. The casing 21 is then moved to the right (viewing FIGURE 1) to close the auxiliary specimen chamber 13 by the cover 23. The knob 33 is again rotated so that the second deflecting coil assembly 26 is in line with the optical axis of the instrument. The handle 48 is again rotated to lock the coil assembly in position.

An electron beam passing down the optical axis of the instrument is deflected by the first deflection coil assembly 4, passes through the aperture 22 of the casing 21 and is deflected again by the second deflection coil assembly 26. The deflected beam irradiates on the surface of the specimen in the cartridge 19 and passes through the apertures 40 and 41 of the objective lens pole pieces 38 and 39 and finally forms a dark field image on a screen (not shown).

By the deflection coil system just described the beam is tilted up to a maximum tilting angle of 6.

FIGURE 2 shows a modified form of our invention in which a casing 21 is not used and in which the cover 23 for the auxiliary specimen chamber is openated independently of the deflection coil system by suitable mechanism (not shown). In the apparatus shown in FIGURE 2 both deflection coil assemblies 4 and 26 are mounted on the yoke 28 which in turn is mounted on the rod 30 and are moved within the main specimen chamber 32 by rotation of the knob 33.

Alternatively the first deflection coil assembly 4 may be mounted on the undersurface of the flange 11 of the condenser lens.

The operation of the modification shown in FIGURE 2 is similar to that described with reference to FIGURE 1. When the specimen cartridge 19 is placed on the specimen stage 20, the deflection coil assemblies are moved toward the left (viewing FIGURE 2) of the main specimen chamber 32. The specimen cartridge is inserted in the auxiliary specimen chamber 13 by the rod 15. After evacuating the auxiliary specimen chamber 13 by conventional means, the cover 23 is opened and the specimen cartridge is placed on the specimen stage 20. Thereafter the deflection coil assemblies are moved to their operating positions in the main specimen chamber 32; as shown in I U E While we have described certain presently preferred embodiments of our invention, it is to be understood that it may be otherwise embodied within the scope of the appended claims.

We claim:

1. An electron beam deflecting apparatus for an electron microscope having a condensing lens and an objective lens comprising:

(A) two electron beam deflection coils mounted along the optical axis of the microscope,

(B) a main specimen chamber extending transversely of the optical :axis of the microscope and positioned between the condensing lens and the objective lens of the microscope,

(C) at least one of said electron beam deflection coil assemblies being located as near as possible to the position at which a specimen is to be positioned in the chamber and mounted for rotation within said chamber and for movement longitudinally of said chamber, and

(D) means perpendicular to said optical axis extending into said chamber and secured to said coil assembly for rotating said coil assembly about an axis perpendicular to said optical axis and moving said coil assembly in a direction perpendicular to said optical axis.

2. An electron beam deflecting apparatus as described in claim 1 in which both electron beam deflection coils are mounted on said means (D of claim 1 for rotation and longitudinal movement within said specimen chamber.

3. An electron beam deflecting apparatus as described in claim 1 and having an [auxiliary specimen chamber adjacent said main specimen chamber and means for providing and closing off access to the main specimen chamber from the auxiliary specimen chamber.

4. An electron beam deflecting apparatus as described in claim 1 and having casing forming a part of said assembly and within the main specimen chamber on which said electron beam deflection coil is mounted, said casing being mounted on means comprising an arm which extends out of the microscope and has an end which can be grasped to rotate and move said electron beam deflection coil.

5. An electron beam deflecting apparatus as described in claim 4 and having an auxiliary specimen chamber adjacent the main specimen chamber and in which a cover is secured to said casing whereby movement of said casing with cover opens and closes said auxiliary specimen chamber to said main specimen chamber.

References Cited UNITED STATES PATENTS 1/1964 Brunnee. 4/1967 Schmidt et a1. 

